MODIFICATION OF THE LAMELLAR PHASE IN C12E5 WATER SYSTEM BY A RANDOM HYDROPHILIC-HYDROPHOBIC POLYELECTROLYTE/

The microstructure of a ternary system of a non-ionic surfactant (n-do decyl pentaoxyethylene glycol ether, C12E5), water and a water-soluble random heteropolymer, poly (styrene-r-Na styrene sulfonate) with degr ees of sulfonation ranging from 30% to 90% is investigated at room tem perature. Using small angle X-ray scattering and freeze-fracture elect ron microscopy we focus on the lamellar phase region and study samples along four different paths of constant surfactant-to-water ratio with increasing polymer content;. We demonstrate that for samples with low water content (S/W ratios 3.4 and 4.9), regardless of the sulfonation degree of the polymer, the lamellar phase persists up to several weig ht percent of polymer and the polymer molecules are confined inside th e surfactant bilayers. With increasing quantity of polymer the lamella r phase Bragg peak shifts in a manner consistent with the increase of the lamellar period, which indicates increased bilayer thickness. For mixtures less concentrated in surfactant first order phase transitions are observed for all polymer charge contents when the amount of polym er is increased. For low charge contents of polymer (30% and 45%) the lamellar stack of the polymer-doped surfactant bilayers coexists with either cubic or another lamellar phase and microscopic phase separatio n is only observed. For large charge contents (65% and 90%) a surfacta nt-rich lamellar phase coexists with a polymer-rich water solution. It is suggested that the observed phase behaviour is governed by the con centration number of free water molecules.